Each nation has a religion, but only the religious nations spread it. Some religious nations are completely zealous, while other try to go diplomatic. Religious nations have a god named Spode and talk about the Source, as shown when contacting an unhappy religious nation, they may say "The Source frowns on your people."

When religious vehicles try to convert a city, they must set up a hologram which will preach to the targeted city. The citizens will usually throw rocks at the vehicles and try to destroy them. Religious vehicles usually target entertainment buildings and turrets, because cities with low happiness are easier to convert. As the religious takeover bar progresses, more and more citizens will start worshipping the hologram and in a way mock the City hall. That means they are about to switch religions.